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Coordinate Referencing System - How the System Works

globe

Precise measurements from each control point are stored in the NSCRS database. These points represent exact locations on the irregularly shaped Earth.

globe2

The Earth's irregular shape is replaced by a geometric shape (ellipsoid) upon which computations are made at various points.

globe3

A cylinder is placed around the Earth and the computed points are transfered from the globe onto the cylinder's surface.

flat map
The cylinder is unrolled, producing a two dimensional map.
   
There is no way to accurately portray a round, three-dimensional object on a flat, two-dimensional piece of paper. Since the Earth is not perfectly round and flat, any attempt to represent the Earth on paper will distort shape, distance, or direction. Older world map projections, for instance, would shrink Africa (near the equator) and expand Canada (near the pole), creating an unrealistic difference in apparent size. Although such inaccuracies are not normally noticeable on a map of Nova Scotia specifically, it is important to understand they exist and they are taken into consideration when maps are produced.

A datum is a three-dimensional coordinate system which has a defined point of origin and orientation and a specific mathematical figure (ellipsoid) defined. Simply put, it is used to calculate where the real world coordinate points should be in relation to each other on the two-dimensional map. As new methods of measuring and gathering information have improved, new datums have evolved to meet these changing needs.

The NSCCS uses the Average Terrestrial System of 1977 (ATS77), while the new NSHPN uses the North American Datum NAD83 (CSRS).

The province has used the 3 Modified Transverse Mercator as its standard with the ATS77 (and earlier) datum. With the new NAD83 datum, the province will move to the 6 UTM projection, bringing Nova Scotia in line with other jurisdictions, including the federal government.

 


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